Westside at Buttercup Creek
Westside news Volume 6, Number 12
Official Newsletter of the Westside at Buttercup Creek HOA
December 2015
NATUREWATCH: WINTRY WONDERS
by Jim and Lynne Weber As temperatures cool further ‘hoar’ comes from an Old English adjective meaning ‘showing signs and autumn turns to winter, of old age’, and refers to the frost making the vegetation look like it our thoughts turn to visions of has grown white hair. When hoar frost forms on objects above the ice and snow. From first frost to surface, like branches and leaves, it has a feathery-like appearance ice storms to snow storms, these and is specifically called air hoar. frozen precipitation events are Snow, on the other hand, is an entirely different matter. When sporadic in Central Texas, but a cold water droplet freezes onto a pollen or dust particle high in when they occur, they can also the sky, it creates an ice crystal. As this primary crystal falls toward be spectacular! the ground, more water vapor freezes on it, building new crystals How does frost, this sparkling layer that sometimes covers the that form the six characteristic arms of a snowflake. This process landscape, form? When the temperature of the air reaches a point of crystallization builds in a symmetrical or patterned way, because where the water vapor in it can condense out into water, it is called it reflects the internal order of the water molecules as they arrange the dew point. The frost point is when the dew point falls below themselves in pre-determined spaces to form the six-sided snowflake. freezing, and rather than producing dew, it creates frost. Consisting The most significant factor that determines the basic shape of of tiny, spike-like crystal structures called ‘spicules’ that grow out from the ice crystal is the temperature at which it forms, and to a lesser a solid surface, frost generally forms on surfaces that are colder than degree humidity. The intricate shape of a single arm of a snowflake the surrounding air. Even the size of the crystals can vary, depending is determined by these atmospheric conditions as the entire crystal upon the amount of time they took to grow, the relative changes in falls. As slight changes in temperature and humidity occur minutes temperature, and the amount of water vapor available. or even seconds later, a crystal that begin to grow in one way might Cold air is denser than warm air, so quite often when night skies then change and branch off in a new direction. Since all six arms of are clear and calm, lower areas become colder due to differences in a snowflake experience the same changes in atmospheric conditions, elevation. Known as surface temperature inversion, this phenomenon they all grow identically. And since individual snowflakes encounter forms ‘frost pockets’ or areas where frost forms first, due to cold slightly different atmospheric conditions as they take different paths air trapped against the ground. On such days, there can be a 40 to the ground, they all tend to look unique, resembling everything to 50 degree difference in air temperature between dawn and early from simple prisms and needles to intricately faceted plates and afternoon. Getting out early can reward you with a rare and wonderful stellar dendrites. spectacle of nature when something called ‘hoar frost’ is formed. On the surface, winter may seem as if nature is shutting down Referring to white ice crystals that are deposited on the ground around us, but take the time for a second look. Aside from the or loosely attached to exposed objects such as leaves and branches, visual beauty they provide, the frosts and snows of the season are just hoar frost forms on cold, clear nights when heat radiates out to the another part of the ongoing cycle of life and renewal for our native open sky faster than it can be replaced by nearby sources such as plants and animals. wind. This allows objects in the landscape to cool below the frost Send your nature-related questions to naturewatch@austin. point of the surrounding air, and well below the freezing point of rr.com and we’ll do our best to answer them. Check out our blog at water. Hoar frost can form in low-lying cold air even when the air naturewatchaustin.blogspot.com if you enjoy reading these articles! temperature a few feet above ground is well above freezing. The name Copyright © 2015 Peel, Inc.
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